Electronic products typically have electrical circuitry implemented on a circuit substrate, such as a printed circuit board. The performance of the circuitry may be adversely affected by factors such as electromagnetic interference (EMI), radio frequency interference (RFI), electrostatic discharge (ESD), and environmental elements. The sources of interference may be internal or external to the product. For example, many electrical components emit radio frequency (RF) signals which may adversely affect the operation of other portions of the circuitry. Moreover, these RF signals may cause interference for other electronic devices operating nearby.
Typically, a product designer incorporates shields, or other protective devices, to protect critical portions of the circuitry, or specific components. For example, to protect against EMI, a critical component is enclosed in EMI shield formed to substantially enclose the component and onto the circuit substrate. Components having a high EMI output are identified and electromagnetically isolated using EMI shields. Moreover, the shield components may be a part of a larger electrical module, such as power amplifier, which is preferably housed in EMI shielded enclosures to provide further protection.
Prior art shielding techniques include metal cans, metal foil claddings, wire mesh screens, and plastic enclosures or cases having metalized coatings. However, several problems associated with prior art shielding techniques need to be overcome. For example, a product may have many components requiring EMI shielding from other components within the product as well as from external sources. Depending on the number of the shields needed, significant weight and cost may be added to the product. Moreover, space must be allocated on the circuit board to accommodate the shields which reduces the space available for other components. Additionally, prior art shielding techniques typically do not facilitate shielding decisions made late in the product design cycle, which may be necessary after product testing. Consequently, major redesigns may be needed to add shields where the need was unanticipated.
The trend toward increasingly smaller products minimizes the space available on the circuit board for many of the shields typically used in the prior art. Cost, weight, and design convenience are also important factors in evaluating shielding options. These and other issues make prior art shielding techniques inadequate for some applications. Therefore, there exists a need for a new approach to EMI and other types of shielding .